Hey Mathias,
Thanks for the input on the eyes, my programmer and I haven't been seeing eye to eye on them.
Right for my mock ups, I'll break the tileset out in photoshop using smart objects (if you're unfamilair with photoshop smartobjects are just linked objects), and then use a program called Tiled ::
http://www.mapeditor.org/ :: for creating the actual tilemaps. Tiled is really awesome tilemapping program. It's not the best out there (DAME is what I would like to be using) but tiled works great with XNA games and it's what my programmer wanted to use so we went with that. A nice feature that tiled does have is to save the map out as an image which I can then load up in photoshop to do my mocks.